Collision of Excitation Waves in the Dog Purkinje System

The ventricular conduction system of the dog was explored with a 50µ extracellular electrode in an in vitro preparation with an intact right and left ventricular bundle branch system connected at the bundle of His. Two pacing electrodes at opposite ends of a functionally single strand produced collision of excitation waves with a distinctive extracellular wave form (uniphasic and positive instead of biphasic). The only changes in the intracellular potential associated with collision were a decrease in the time constant of the foot and an increase in the maximum rate of rise of the action potential, changes not uniquely produced hy collisions. During pacing at one point, collisions were detected at many places throughout the conduction system. The peripheral Purkinje system consisted of fine strands forming a network of interconnecting swirls, each covering 2-25 mm 2 Collisions were found in all swirls and their sites often shifted with a shift in the pacemaker site. Collisions also shifted in location between basic and premature beats which originated from a single point on the bundle of His.